This invention is directed to a method of producing single phase metal alloy parts of a wide variety of shapes and a wide variety of alloy compositions by the reduction of metal oxide agglomerates.
The prior art of powder metallurgy teaches the production of metal parts by sintering powders of the desired metal alloy composition. First, the powder is formed into the desired shape, compacted, and then sintered to achieve densification with the time and temperature controlled to give the desired strength and porosity characteristics.
However, several limitations appear from working with metal powders. Firstly, many metal powders are so reactive in air that special steps must be taken to prevent surface oxidation prior to or during final fabrication. Such steps could include the use of inert atmospheres, or reducing the powders to remove surface oxidation just prior to or during fabrication. However, such steps tend to increase the cost of production. To overcome this first problem, metal oxide powders may be used rather than metal powders, with the formed oxide shape being reduced to a metal as the last step. See, for example, Swedish Pat. No. 127,524 and French Pat. No. 1,100,993.
A second limitation is that many mixtures of different metal powders do not readily form as a single phase alloy by sintering alone. To overcome this problem, the prior art requires an annealing step, typically requiring several hours. Alternately, in order to obtain single phase alloys, the metal components may be cooled from a melt in which they exist as a single phase. However, the melt technique loses the advantages of powder metallurgy, and requires generally higher temperatures. The prior art has not obtained complex single-phase shaped parts by the reduction of mixed oxides, but see "Sintering Phenomenon in Compacted Iron Powder (II)" by T. Nishijima, J. Japan Soc. Powder Metallurgy, 6 (1):19-24 (1959) for two component systems.
Clearly, it would be desirable to have a technique by which the advantages of powder metallurgy are realized in obtaining single phase metal alloy articles while avoiding long annealing times, and at the same time enjoying the advantages of working with oxide powders.